A gas turbine engine such as that used for powering an aircraft in flight includes a combustor which generates hot combustion gases, with the discharge therefrom flowing through a high pressure turbine nozzle which directs the combustion gases to a row of turbine rotor blades which extract energy therefrom for rotating a disk and shaft joined thereto for typically powering a compressor of the engine. The first stage turbine rotor blades receive the hottest combustion gases in the engine and are therefore typically hollow and provided with various structures used for providing effective cooling thereof for ensuring useful operating lives therefor.
The turbine rotor blades typically include serpentine flow passages therein and various cooling holes through the airfoil pressure side, suction side, or tip as required. Cooling air is provided to the blade by bleeding a portion of relatively cool compressor air and suitably channeling it through the blade dovetail and into the blade for supplying the cooling structures therein. However, any air bled from the compressor which is used for cooling purposes is not therefore used in the combustion process which necessarily decreases the overall efficiency of the engine. It is therefore desirable to use as little as possible of compressor bleed flow for cooling purposes.
One type of cooling hole found in either rotor blades or stator vanes is a pressure side, ejection slot extending parallel to the engine centerline which is typically also perpendicular to the longitudinal or radial axis of the blade airfoil. Cooling air is discharged from the inside of the airfoil and out the ejection slots in an aft direction for providing film cooling of the trailing edge region of the airfoil. Recent analytical evaluation of the combustion gas flow field flowing over the pressure side of the airfoil and visual inspection of airfoils operated in an engine have shown that the combustion gas streamlines migrate both radially outwardly and radially inwardly from the pitchline or mid-span of the airfoil which has led to improvements in airfoil cooling in accordance with the present invention described below.